1. Technical Field
The present invention relates to a turbine used in, for example, a power generation plant, a chemical plant, a gas plant, steelworks, a ship, or the like.
Priority is claimed on Japanese Patent Application No. 2010-217218, filed on Sep. 28, 2010, the content of which is incorporated herein by reference.
2. Background Art
In the related art, as one kind of a steam turbine, a steam turbine including a casing, a shaft body (rotor) rotatably installed in the casing, turbine vanes fixedly disposed at an inner circumferential section of the casing, and turbine blades radially installed at the shaft body in a downstream side of the turbine vanes, which are provided in a plurality of stages, is well-known. The steam turbine is generally classified as an impulse turbine or a reaction turbine according to a difference in operation type. In the impulse turbine, the turbine blades are rotated only by an impulsive force received from steam.
In the impulse turbine, the turbine vanes have a nozzle shape, steam passing through the turbine vanes is injected to the turbine blades, and the turbine blades are rotated only by an impulsive force received from the steam. Meanwhile, in the reaction turbine, the turbine vanes have the same shapes as the turbine blades, and the turbine blades are rotated by an impulsive force received from the steam passing through the turbine vanes and a reactive force with respect to expansion of the steam generated when passing through the turbine blades.
Here, in such a steam turbine, a clearance having a predetermined width in a radial direction is formed between tip sections of the turbine blades and the casing, and a clearance having a predetermined width in the radial direction is also formed between tip sections of the turbine vanes and the shaft body. Then, some of the steam flowing in an axial direction of the shaft body is leaked to a downstream side through the clearances with the tip sections of these turbine blades or the turbine vanes. Here, since the steam leaked downstream from the clearance between turbine blades and the casing applies neither the impulsive force nor the reactive force with respect to the turbine blades, the steam hardly contributes to a driving force to rotate the turbine blades regardless of the impulse turbine or the reaction turbine. In addition, since the steam leaked from the clearance between the turbine vanes and the shaft body to the downstream side is neither varied in velocity nor expanded even when passing over the turbine vanes, the steam hardly contributes to a driving force to rotate the turbine blades of the downstream side regardless of the impulse turbine or the reaction turbine. Accordingly, in order to improve performance of the steam turbine, it is important to reduce a leakage amount of the steam in the clearance with the tip sections of the turbine blade or the turbine vane.
Here, a seal fin is conventionally used as a means for preventing a leakage of the steam from the clearance with the tip sections of the turbine blades or the turbine vanes. For example, when the seal fin is used at the tip section of the turbine blade, the seal fin is installed to protrude from any one of the turbine blade and the casing and form a small clearance with the other.
In addition, in the steam turbine in the related art, it is known that a casing corner is formed in a curved shape in a cross-section in the axial direction such that a stress concentration is not generated due to thermal expansion or the like of the casing at a corner formed at a wall surface of the casing (for example, see FIG. 2 of Patent Document 1). Here, in general, the curved shape of the casing corner is formed in an arc shape having a radius of about 1 mm.